1. Field of the Invention
The present invention generally relates to an inkjet recording apparatus that can be used as an imaging apparatus, such as a printer, a facsimile machine, and a copier.
2. Description of the Related Art
An inkjet recording apparatus can be used in products such as a printer, a facsimile machine, a copier, a plotter, and a multifunction peripheral combining a number of the above functions. An inkjet recording apparatus performs image formation (recording, printing, and imaging are sometimes synonymously used) by having a recording head discharge ink droplets onto an image recording medium. An image recording medium is not limited to paper, and may include OHP, for example. An image recording medium refers to any medium that is capable of having liquid such as ink droplets or solid matter such as toner adhered thereto. It is noted that the terms “recording medium,” “recording paper,” and “recording sheet” may be synonymously used.
An inkjet recording apparatus refers to an apparatus that performs image formation by discharging liquid onto an image recording medium such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics, for example. It is noted that the term “image formation” is not limited to the rendering of an image such as characters and figures that have meaning onto an image recording medium. Rather, the term broadly encompasses the rendering of any image including an image having no meaning such as a pattern, for example. The term “ink” is not limited to that which is commonly referred to as ink, and broadly encompasses any matter that can be discharged as liquid, including DNA samples, resist, pattern materials, for example. The term “image” is not limited to that which is rendered on a planar surface, and includes an image that is rendered on a three-dimensional object, or an image that is in itself created by structuring a three-dimensional object, for example.
A recording head of an inkjet recording apparatus includes a nozzle that discharges ink droplets, a pressure chamber that is in communication with the nozzle, and pressure generating means that applies pressure on ink within the pressure chamber. The pressure generating means may be made of an electromechanical transduction element such as a piezoelectric element or an electro-thermal element such as a heater, for example. An inkjet recording apparatus forms an image on an image recording medium by applying pressure on ink within the pressure chamber with the pressure generating means and discharging ink droplets from the nozzle of the recording head. An inkjet recording apparatus may be a serial type inkjet recording apparatus that forms an image by having a recording head discharge ink droplets while moving in the main scanning direction, or a line type inkjet recording apparatus that uses a line type head and forms an image by having the recording head discharge ink droplets while the recording head is at a standstill. The serial type inkjet recording apparatus has one or more recording heads for forming an image on an image recording medium mounted on a carriage that moves back and forth in a direction intersecting the image recording medium transporting direction.
Japanese Laid-Open Patent Application No. 2004-066785 discloses a serial type inkjet recording apparatus. This inkjet recording apparatus is arranged to have a recording head that is detachable from the carriage. Configuring the recording head to be detachable from the carriage can contribute to cost reduction through improvement of assemblage efficiency during manufacturing or improvement of applicability when a user replaces the recording head. Also, this inkjet recording apparatus has two head protection plates arranged on the carriage to prevent a folded portion of the recording medium (image recording medium) from getting stuck in the periphery of flexible printed circuits that are mounted on the recording head and causing the flexible printed circuits to peel off, for example. The two head protection boards are arranged close to both sides of the flexible printed circuits in the main scanning direction, and the surfaces of the head protection boards are arranged to protrude further than the surface of the flexible printed circuits. In this way, when scanning the carriage during image formation, even if there is a folded portion of the image recording medium at the front in the scanning direction (main scanning direction), the folded portion will come into contact with the head protection boards rather than the flexible printed circuits so that failure of the recording head can be prevented.
However, the inkjet recording apparatus described in Japanese Laid-Open Patent Application No. 2004-066785 only has head protection plates arranged in the main scanning direction with respect to the nozzle face and does not have head protection plates arranged in the sub-scanning direction. It has been revealed from research by the inventors of the present invention that if the image recording medium has a mound-shaped folded portion viewed from the sub-scanning direction, for example, the top of the folded portion may override the head protection plates and come into contact with the surface of the flexible printed circuits (nozzle face of the recording head) during carriage scanning. When the folded portion of the image recording medium comes into contact with the nozzle face of the recording head, ink adhered to the nozzle face may adhere to the image recording medium thereby causing problems such as degradation of printing quality and failure of the recording head, for example.
The inventors of the present invention have discovered through diligent research that arranging head protection members such as head protection plates not only in the main scanning direction with respect to the nozzle face of the recording head but also in the sub-scanning direction would effectively prevent such problems from occurring. However, it has been revealed that if head protection members are arranged in the main scanning direction and the sub-scanning direction with respect to the nozzle face of the recording head such that the nozzle face is surrounded by head protection members on four sides, the following problems are prone to occur.
In order to ensure printing quality of the inkjet recording apparatus, ink droplets discharged from the nozzle of the recording head must land on the image recording medium with high position accuracy. In an inkjet recording apparatus having a recording head that is detachable from the carriage, the nozzle of the recording head must be positioned with respect to the carriage with high accuracy upon mounting the recording head. A common method for accurately positioning the detachable recording head with respect to the carriage is to mount the recording head to the carriage while a position reference plane arranged at the recording head and a position reference plane arranged at the carriage are in contact with each other. It is noted that in the following, a case in which the position reference planes are configured to position the recording head with respect to the sub-scanning direction is described as an example. However, the same applies to a case in which the position reference planes are configured to position the recording head with respect to the main scanning direction.
To realize the above mounting method, a configuration is desired that enables relative movement of the recording head in the sub-scanning direction with respect to the carriage so that the position reference plane of the recording head faces the position reference plane of the carriage. When head protection members on the carriage are arranged at the sub-scanning direction sides with respect to the nozzle face of the recording head, these head protection members will interfere with the relative movement of the recording head. In turn, the relative movement range of the recording head may be restricted and the relative movement operation of the recording head may be hindered so that it may be difficult to properly mount the recording head to the carriage.
On the other hand, by widening the gap between the two head protection members arranged at the sub-scanning direction sides of the nozzle face of the recording head, an adequate relative movement range for the recording head may be secured so that the relative movement of the recording head may not be hindered. However, in this case, the distance between each head protection member and the nozzle face is increased. When the distance between the head protection member and the nozzle face is increased, the head protection effect of the head protection member will decrease thereby leading to an increased possibility of a folded portion of the image recording medium coming into contact with the nozzle face.
It is noted that the above problem occurs not only in a case where head protection members are arranged at the main scanning direction sides and the sub-scanning direction sides of the nozzle face of the recording head but in any case where head protection members are arranged in the same direction as the relative movement direction of the recording head for arranging the position reference plane of the recording head to face the position reference plane of the carriage when mounting or removing the recording head.